Semiconductor device having schottky diode structure

ABSTRACT

A semiconductor device including a base substrate; a semiconductor layer which is disposed on the base substrate and has a 2-Dimensional Electron Gas (2DEG) generated within the semiconductor layer; a plurality of first ohmic electrodes which are disposed on the central region of the semiconductor layer and have island-shaped cross sections; a second ohmic electrode which is disposed on edge regions of the semiconductor layer; and a Schottky electrode part has first bonding portions bonded to the first ohmic electrodes, and a second bonding portion bonded to the semiconductor layer. A depletion region is provided to be spaced apart from the 2DEG when the semiconductor device is driven at an on-voltage and is provided to be expanded to the 2DEG when the semiconductor device is driven at an off-voltage, the depletion region being generated within the semiconductor layer by bonding the semiconductor layer and the second bonding portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/654,936, filed on Jan. 8, 2010, which claims the benefit of KoreanPatent Application Nos. 10-2009-0080746 and 10-2009-0080747, filed withthe Korea Intellectual Property Office on Aug. 28, 2009, the disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field

The present invention relates to a semiconductor device; and, moreparticularly, to a semiconductor device having a Schottky diodestructure, and a method for manufacturing the same.

2. Description of the Related Art

In general, an active device of semiconductor devices is used toconfigure a circuit, such as an amplifier, a voltage regulator, acurrent regulator, an oscillator, a logic gate, and so on. A diode ofactive devices is widely used as a detecting device, a rectifyingdevice, and a switching device. As for a typical diode, a voltageregulator diode, a variable capacitance diode, a photo diode, a LightEmitting Diode (LED), a zener diode, a gunn diode, a Schottky diode, andso on are exemplified.

The Schottky diode of the exemplified diodes uses Schottky junctiongenerated when a metal comes into contact with semiconductor. TheSchottky diode can implement high-speed switching operation and lowforward voltage driving. The nitride-based semiconductor device like theSchottky diode has a Schottky contact as an anode electrode, and anohmic contact as a cathode electrode. However, in the Schottky diodewith such a structure, there is a trade-off relation betweensatification of low on-voltage and on-current and reduction of a reverseleakage current. Thus, it is difficult to develop a nitride-basedsemiconductor device capable of operating at a low on-voltage andreducing a reverse leakage current.

SUMMARY

The present invention has been proposed in order to overcome theabove-described problems and it is, therefore, an object of the presentinvention to provide a semiconductor device operable at a low on-voltageand a method for manufacturing the same.

Further, another object of the present invention is to provide asemiconductor device for reducing a reverse leakage current and a methodfor manufacturing the same.

Further, another object of the present invention is to provide asemiconductor device for increasing a breakdown current and a method formanufacturing the same.

Further, another object of the present invention is to provide asemiconductor device having a high forward current and a method formanufacturing the same.

In accordance with one aspect of the present invention to achieve theobject, there is provided a semiconductor device including: a basesubstrate; a semiconductor layer which is disposed on the base substrateand has a 2-Dimensional Electron Gas (2DEG) formed therewithin; a firstohmic electrode disposed on a central region of the semiconductor layer;a second ohmic electrode which is formed on the edge regions of thesemiconductor layer in such a manner to be disposed to be spaced apartfrom the first ohmic electrodes, and have a ring shape surrounding thefirst ohmic electrode; and a Schottky electrode part which is formed onthe central region to cover the first ohmic electrode and is formed tobe spaced apart from the second ohmic electrode.

The first ohmic electrode is bonded to the semiconductor layer of thecentral regions to thereby come into ohmic contact with thesemiconductor layer, the second ohmic electrode is bonded to thesemiconductor layer of the edge regions to thereby come into ohmiccontact with the semiconductor layer, and the Schottky electrode part isbonded to the semiconductor layer on the middle regions between thecentral region and the edge regions to thereby come into ohmic contactwith the semiconductor layer.

The semiconductor layer includes: a first nitride film which is disposedon the base substrate and has GaN material; and a second nitride filmwhich is disposed on the first nitride film and has AlGaN material.

The Schottky electrode part includes: a central portion which covers atop surface of the first ohmic electrode; and edge portions which coverthe semiconductor layer adjacent to a circumstance of the first ohmicelectrode, wherein the edge portions of the Schottky electrode part areextended into the semiconductor layer.

The semiconductor layer includes: a first nitride film on the basesubstrate; a second nitride film which is disposed on the first nitridefilm and has an energy band gap wider than that of the first nitridefilm, wherein the edge portions of the Schottky electrode part areextended into the second nitride film, and are formed to be spaced apartfrom the first nitride film.

The semiconductor layer includes: a first nitride film formed on thebase substrate; a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the edge portions are extended into the firstnitride film through the second nitride film.

The semiconductor layer includes: a first nitride film formed on thebase substrate; a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the first ohmic electrode is extended into thesecond nitride film and is formed to be spaced apart from the firstnitride film.

The semiconductor layer includes: a first nitride film formed on thebase substrate; a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the first ohmic electrode is extended into thesecond nitride film through the first nitride film.

The semiconductor device further includes a filed plate disposed betweenthe first ohmic electrode and the second ohmic electrode.

The field plate has internal side portions covered by the Schottkyelectrode, and external side portions covered by the second ohmicelectrode, and central portions exposed.

In accordance with another aspect of the present invention to achievethe object, there is provided a semiconductor device including: a basesubstrate; a semiconductor layer which is disposed on the base substrateand has a 2DEG generated therewithin; a first ohmic electrode disposedon the central region of the semiconductor layer; a second ohmicelectrode disposed on the edge regions of the semiconductor layer; and aSchottky electrode part provided with central portions bonded to thefirst ohmic electrode and edge portions bonded to the semiconductorlayer, wherein a depletion region is provided to be spaced apart fromthe 2DEG when the semiconductor device is driven at an on-voltage, andis provided to be expanded to the 2DEG when the semiconductor device isdriven at an off-voltage, the depletion region being generated withinthe semiconductor layer by bonding the semiconductor layer and the edgeportions.

The central portion of the Schottky electrode part is disposed on a toppart of the first ohmic electrode, and the edge portions of the Schottkyelectrode part are provided to be bonded to the semiconductor layeradjacent to a circumstance of the first ohmic electrode.

When the semiconductor device is driven at a forward voltage equal to orhigher than the on-voltage of the Schottky electrode part, the depletionregion is provided to allow a current to flow from the Schottkyelectrode part to the 2DEG.

When the semiconductor device is driven at a forward voltage lower thanthe on-voltage of the Schottky electrode part, the depletion regionblocks a current flow from the Schottky electrode part to the 2DEG.

When the semiconductor device is driven at a reverse voltage, thedepletion region blocks a current flow from the first ohmic electrode tothe 2DEG.

In accordance with another aspect of the present invention to achievethe object, there is provided a method for manufacturing a semiconductordevice including the steps of: preparing a base substrate; forming asemiconductor layer, which generates a 2DEG within the semiconductorlayer, on the base substrate; forming a first ohmic electrode on acentral region of the semiconductor layer; forming a second ohmicelectrode having a ring shape surrounding the first ohmic electrode, onthe edge regions of the semiconductor layer; and forming a Schottkyelectrode part, which entirely covers the first ohmic electrode and arespaced apart from the second ohmic electrode, on the semiconductorlayer.

The step of forming the first ohmic electrode and the step of formingthe second ohmic electrode are performed in in-situ.

The step of forming the semiconductor layer further includes a step offorming recesses on the semiconductor layer adjacent to a circumstanceof the first ohmic electrode, after forming the first ohmic electrode,and the step of forming the Schottky electrode comprises a step ofburring a metallic material different form that of the first ohmicelectrode into the recesses.

The step of forming the semiconductor layer further includes a step offorming recesses on the central region and the edge regions of thesemiconductor layer, before forming the first ohmic electrode, and thestep of forming the first ohmic electrode and the step of forming thesecond ohmic electrode comprise a step of burring a metallic materialdifferent form that of the Schottky electrode into the recesses.

The method further includes a step of forming a field plate on middleregions between the central region and the edge regions of thesemiconductor layer.

The step of forming the second ohmic electrode includes the steps of:forming a first metal film on the semiconductor layer; at least forminga first photoresist pattern exposing the first metal film on externalside portions of the field plate; and etching the first metal film byusing the first photoresist pattern as an etching mask, wherein the stepof forming the Schottky electrode comprises the steps of: forming asecond metal film different from the first metal film on thesemiconductor layer after forming the second ohmic electrode; at leastforming a second photoresist pattern exposing the second metal film oninternal side portions of the field plate; and etching the second metalfilm by using the first photoresist pattern as an etching mask.

In accordance with another aspect of the present invention to achievethe object, there is provided a semiconductor device including: a basesubstrate; a semiconductor layer which is disposed on the base substrateand has a 2DEG generated within the semiconductor layer; a plurality offirst ohmic electrodes with a shape protruded upward from a centralregion of the semiconductor layer; a second ohmic electrode with a ringshape formed along the edge regions of the semiconductor layer; and aSchottky electrode part which is formed to be spaced apart from thesecond ohmic electrode and covers the first ohmic electrode to therebyhave a prominence and depression structure in which the Schottkyelectrode part is engaged with the first ohmic electrode up and down.

The first ohmic electrodes are disposed to be arranged in a latticeconfiguration within the Schottky electrode part.

The first ohmic electrode has a ring shape based on the center of thesemiconductor layer, and the first ohmic electrodes each has a diameterdifferent from one another.

The first ohmic electrodes are bonded to the semiconductor layer in thecentral region to thereby come into ohmic contact with the semiconductorlayer, the second ohmic electrode is bonded to the semiconductor layerin the edge regions to thereby come into ohmic contact with thesemiconductor layer, and the Schottky electrode is bonded to thesemiconductor layer adjacent to the first ohmic electrodes to therebycome into ohmic contact with the semiconductor layer.

The semiconductor layer includes: a first nitride film which is disposedon the base substrate and has GaN material; and a second nitride filmwhich is disposed on the first nitride film and has AlGaN material.

The Schottky electrode part is extended into the semiconductor layer andhas a height lower than that of a bottom surface of the first ohmicelectrodes.

The semiconductor layer includes: a first nitride film formed on thebase substrate; and a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the Schottky electrode part is extended to insideof the second nitride film and is spaced apart from the first nitridefilm.

The semiconductor layer includes: a first nitride film formed on thebase substrate; and a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the Schottky electrode part is extended to insideof the first nitride film through the second nitride film.

The semiconductor layer includes: a first nitride film formed on thebase substrate; and a second nitride film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the first ohmic electrodes are extended to insideof the second nitride film and is spaced apart from the first nitridefilm.

The semiconductor layer includes: a first nitride film formed on thebase substrate; and an energy film which is disposed on the firstnitride film and has an energy band gap wider than that of the firstnitride film, wherein the first ohmic electrodes are extended to insideof the second nitride film and are spaced apart from the first nitridefilm.

The semiconductor device further includes a field plate including aninsulating film disposed between the first ohmic electrodes and thesecond ohmic electrode.

The field plat has internal side portions covered by the Schottkyelectrode, external side portions covered by the second ohmicelectrodes, and central portions exposed.

In accordance with another aspect of the present invention to achievethe object, there is provided a semiconductor device including: a basesubstrate; a semiconductor layer which is disposed on the base substrateand has a 2-Dimensional Electron Gas (2DEG) generated within thesemiconductor layer; a plurality of first ohmic electrodes which aredisposed on the central region of the semiconductor layer and haveisland-shaped cross sections; a second ohmic electrode which is disposedon edge regions of the semiconductor layer; and a Schottky electrodepart has first bonding portions bonded to the first ohmic electrodes,and a second bonding portion bonded to the semiconductor layer, whereina depletion region is provided to be spaced apart from the 2DEG when thesemiconductor device is driven at an on-voltage and is provided to beexpanded to the 2DEG when the semiconductor device is driven at anoff-voltage, the depletion region being generated within thesemiconductor layer by bonding the semiconductor layer and the secondbonding portion.

The Schottky electrode part has a prominence and depression structure inwhich the Schottky electrode part is engaged with the first ohmicelectrodes up and down.

The first bonding portions are bonded to the first ohmic electrodes on atop part of the first ohmic electrodes, and the second bonding portionis bonded to a region of the semiconductor layer adjacent to the firstohmic electrodes.

When the semiconductor device is driven at a forward voltage equal to orhigher than the on-voltage of the Schottky electrode part, the depletionregion is provided to allow a current to flow from the Schottkyelectrode part to the 2DEG.

When the semiconductor device is driven at a forward voltage lower thanthe on-voltage of the Schottky electrode part, the depletion regionblocks a current flow from the Schottky electrode part to the 2DEG.

When the semiconductor device is driven at a reverse voltage, thedepletion region blocks a current flow from the first ohmic electrodesto the 2DEG.

In accordance with another aspect of the present invention to achievethe object, there is provided a method for manufacturing a semiconductordevice including the steps of: preparing a base substrate; forming asemiconductor layer, which have a 2DEG generated within thesemiconductor layer, on the base substrate; forming a plurality of firstohmic electrodes with a shape, protruded upward from the semiconductorlayer, on a central region of the semiconductor layer; forming a secondohmic electrode having a ring shape formed along edge regions of thesemiconductor layer; and forming a Schottky electrode part whichentirely covers the first ohmic electrodes to thereby have a depressionstructure in which the Schottky electrode part is engaged with pillarsof the electrodes up and down.

The step of forming the semiconductor layer further comprises a step offorming recesses on a region of the semiconductor layer adjacent to thefirst ohmic electrodes, after forming the first ohmic electrodes, andthe step of forming the Schottky electrode comprises a step of burringmetallic materials different form those of the first ohmic electrodesinto the recesses.

The step of forming the recesses further includes the steps of: forminga photoresist pattern, exposing regions of the semiconductor layeradjacent to the first ohmic electrodes, on the semiconductor layer; andetching the semiconductor layer by using the photoresist pattern as anetching mask.

The method further includes a step of forming recesses on the centralregion and the edge regions of the semiconductor layer before the firstohmic electrodes are formed, and wherein the step of forming the firstohmic electrodes and the second ohmic electrodes comprises a step ofburring metallic material different from that of the Schottky electrodepart into the recesses.

In the step of forming the recesses, a plurality of contact holesdisposed to be in a lattice configuration are formed on the centralregion.

In the step of forming the recesses, a trench having a ring shape basedon a center of the semiconductor layer is formed on the semiconductorlayer.

The method further includes a step of forming a field plate on middleregions between the central region and the edge regions of thesemiconductor layer.

The step of forming the second ohmic electrodes includes the steps of:forming a first metal film on the semiconductor layer; at least forminga first photoresist pattern exposing the first metal film on externalside portions of the field plate; and etching the first metal film byusing the first photoresist pattern as an etching mask, wherein the stepof forming a Schottky electrode comprises the steps of: forming a secondmetal film different from the first metal film after forming the secondohmic electrode; at least forming a second photoresist pattern exposingthe second metal film on the internal side portions of the field plate;and etching the second metal film by using the second photoresistpattern as an etching mask.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a plane-view showing a semiconductor device in accordance withone embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1;

FIGS. 3A to 3C are views showing operation states of the semiconductordevice shown in FIG. 1, respectively;

FIGS. 4A to 4C are views showing methods for manufacturing thesemiconductor device in accordance with one embodiment of the presentinvention, respectively;

FIG. 5 is a plane-view showing a modified example of a semiconductordevice in accordance with one embodiment of the present invention;

FIG. 6 is a cross-sectional view taken along a line II-II′ of FIG. 5;

FIGS. 7A to 7C are views showing a method for manufacturing thesemiconductor shown in FIGS. 5 and 6;

FIG. 8 is a plane-view showing other modified example of a semiconductordevice shown in FIGS. 1 and 2;

FIG. 9 is a cross-sectional view taken along a line III-III′ of FIG. 8;

FIGS. 10A to 10C are views showing a method for manufacturing thesemiconductor shown in FIGS. 8 and 9;

FIG. 11 is a plane-view showing other modified example of asemiconductor device shown in FIGS. 1 and 2;

FIG. 12 is a cross-sectional view taken along a line IV-IV′ of FIG. 11;

FIGS. 13A to 13C are views showing a method for manufacturing thesemiconductor shown in FIGS. 11 and 12;

FIG. 14 is a plane-view showing other modified example of asemiconductor device shown in accordance with other embodiment of thepresent invention;

FIG. 15 is a cross-sectional view taken along a line V-V′ of FIG. 14;

FIGS. 16A to 16C are, views showing a method for manufacturing thesemiconductor shown in FIG. 14;

FIGS. 17A to 17C are views showing other modified example of asemiconductor device shown in accordance with other embodiment of thepresent invention;

FIG. 18 is a plane-view showing other modified example of asemiconductor device shown in accordance with other embodiment of thepresent invention;

FIG. 19 is a cross-sectional view taken along a line VI-VI′ of FIG. 18;

FIGS. 20A to 20C are views showing a method for manufacturing thesemiconductor having been described with reference to FIGS. 18 and 19;

FIG. 21 is a plane-view showing other modified example of asemiconductor device in accordance with other embodiment of the presentinvention;

FIG. 22 is a cross-sectional view taken along a line VII-VII′ of FIG.21;

FIG. 23 is a plane-view showing other modified example of asemiconductor device shown in FIG. 21;

FIGS. 24A to 24C are views showing a method for manufacturing thesemiconductor shown in FIGS. 21 and 22;

FIG. 25 is a plane-view showing other modified example of asemiconductor device in accordance with other embodiment of the presentinvention;

FIG. 26 is a cross-sectional view taken along a line VIII-VIII′ of FIG.25;

FIGS. 27A to 27C are views showing a method for manufacturing thesemiconductor shown in FIGS. 25 and 26;

FIG. 28 is a plane-view showing other modified example of asemiconductor device in accordance with other embodiment of the presentinvention;

FIG. 29 is a cross-sectional view taken along a line IX-IX′ of FIG. 28;

FIGS. 30A to 30C are views showing a method for manufacturing thesemiconductor shown in FIGS. 28 and 29;

FIG. 31 is a plane-view showing other modified example of asemiconductor device in accordance with other embodiment of the presentinvention; and

FIG. 32 is a cross-sectional view taken along a line X-X′ of FIG. 31.

DESCRIPTION OF EMBODIMENTS

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Preferred embodiments of the invention will be described below withreference to cross-sectional views, which are exemplary drawings of theinvention. The exemplary drawings may be modified by manufacturingtechniques and/or tolerances. Accordingly, the preferred embodiments ofthe invention are not limited to specific configurations shown in thedrawings, and include modifications based on the method of manufacturingthe semiconductor device. For example, an etched region shown at a rightangle may be formed in the rounded shape or formed to have apredetermined curvature. Therefore, regions shown in the drawings haveschematic characteristics. In addition, the shapes of the regions shownin the drawings exemplify specific shapes of regions in an element, anddo not limit the invention.

Hereinafter, a detailed description will be given of a semiconductordevice and a method for manufacturing the same in accordance withembodiments of the present invention, with reference to accompanyingdrawings.

FIG. 1 is a plane-view showing a semiconductor device in accordance withone embodiment of the present invention, and FIG. 2 is a cross-sectionalview taken along a line I-I′ of FIG. 1.

Referring to FIGS. 1 and 2, the semiconductor device 100 may include abase substrate 110, a semiconductor layer 120, an ohmic electrode part130, a Schottky electrode part 140.

The base substrate 110 may be a plate used for formation of thesemiconductor device having a Schottky diode structure. For example, thebase substrate 110 may be a semiconductor substrate. The base substrate110 may correspond to at least one of a silicon substrate, a siliconcarbide substrate, and a sapphire substrate.

The semiconductor layer 120 may be disposed on the base substrate 110.For example, the semiconductor layer 120 may include a first nitridefilm 122 and a second nitride film 124 which are sequentially stacked onthe base substrate 110. The second nitride film 124 may be formed of amaterial having an energy band gap wider than that of the first nitridefilm 122. In addition, the second nitride film 124 may be formed of amaterial having a lattice parameter different from that of the firstnitride film 122. For example, the first nitride film 122 and the secondnitride film 124 may be films which contain a III-nitride-basedmaterial. In particular, the first nitride film 122 and the secondnitride film 124 may be formed of any one of GaN, AlGaN, InGaN, andInAlGaN. For example, the first nitride film 122 may be a galliumnitride film, and the second nitride film 124 may be an aluminiumgallium nitride film. Herein, the first nitride film 122 of thesemiconductor layer 120 is formed of P-type GaN having high resistivity,thereby reducing a leakage current of the semiconductor device 100.

In the semiconductor layer 120 with the above-described structure, a2-Dimensional Electron Gas (2DEG) may be generated on the boundary ofthe first nitride film 122 and the second nitride film 124. When thesemiconductor device 100 is operated, a current flows through the 2DEG.Meanwhile, a buffering film (not shown) may be further provided betweenthe base substrate 110 and the first nitride film 122 so as to solveproblems caused by lattice mis-match generated between the basesubstrate 110 and the first nitride film 122.

The ohmic electrode part 130 may be disposed on the second nitride film124. For example, the ohmic electrode part 130 may include a first ohmicelectrode 132 and a second ohmic electrode 134. The first ohmicelectrode 132 may be disposed on a central region A1 of the secondnitride film 124. The second ohmic electrode 134 may be disposed on edgeregions A2 of the second nitride film 124 so that it can surround thefirst ohmic electrode 132. Thus, the second ohmic electrode 134 may begenerally formed in a ring shape. Also, the second ohmic electrode 134may be disposed to be spaced apart from the first ohmic electrode 132 ata predetermined space.

The Schottky electrode part 140 may be provided to cover the first ohmicelectrode 132. For example, the Schottky electrode part 140 may beprovided on the central region A1 of the second nitride film 124 so thatit can entirely cover the first ohmic electrode 132. Thus, the centralportion 142 of the Schottky electrode part 140 covers a top surface ofthe first ohmic electrode 132, and the edge portions 144 of the Schottkyelectrode part 140 may cover side surfaces of the first ohmic electrode132. In addition, the edge portions 144 of the Schottky electrode part140 may cover a part of the second nitride film 124 exposed to middleregions A3 between the central region A1 and the edge regions A2.Herein, the edge portions 144 of the Schottky electrode part 140 may beprovided to be spaced apart from the second ohmic electrode 134,respectively.

In the semiconductor device 100 having the same structure, the firstohmic electrode 132 comes into ohmic contact with the second nitridefilm 124 in the central region A1, and the second ohmic electrode 134comes into ohmic contact with the second nitride film 124 in the edgeregions A2. The second nitride film 124 may come into Schottky contactwith the Schottky electrode part 140 in the middle regions A3. Also, theSchottky electrode part 140 may be used as an anode electrode, and thesecond ohmic electrode 134 may be used as a cathode electrode.

Meanwhile, the ohmic electrode part 130 and the Schottky electrode part140 may be formed of various materials. For example, the first ohmicelectrode 132 and the second ohmic electrode 134 may be formed of thesame metallic material, and the Schottky electrode part 140 may beformed of metallic material different from those of the first and secondohmic electrodes 132 and 134. For example, the first and second ohmicelectrodes 132 and 134 may be formed of a metallic material composed ofat least one of Al, Mo, Au, Ni, Pt, Ti, Pd, Ir, Rh, Co, W, Ta, Cu, Zn.On the contrary, the Schottky electrode part 140 may be formed of amaterial composed of one or more metal elements different from that ofthe ohmic electrode part 130. Continuously, a detailed description willbe given of various operation states of the semiconductor device 100 inaccordance with an embodiment of the present invention.

Continuously, a detailed description will be given of various operationstates of the semiconductor device in accordance with one embodiment ofthe present invention having been described with reference to FIGS. 1and 2.

FIGS. 3A to 3C are views showing operation states of the semiconductordevice shown in FIG. 1, respectively. FIG. 3A is a view showing anoperation state of the semiconductor device when driven at a forwardvoltage equal to or higher than an on-voltage of the Schottky diode.Referring to FIG. 3A, when the semiconductor device 100 in accordancewith one embodiment of the present invention is driven at a firstforward voltage equal to or higher than the on-voltage of the Schottkydiode, a depletion region (DR1) generated where the second semiconductorlayer 120 and the Schottky electrode part 140 are joined together may berelatively reduced. Thus, in the semiconductor device 100, a current mayflow through a first current path CP1 and a second current path CP2,wherein the first current path CP1 passes through the 2DEG from thefirst ohmic electrode 132, and the second current path CP2 passesthrough the 2DEG from the Schottky electrode part 140. In this case,since forward currents of the semiconductor device 100 are increased, itis possible to operate the semiconductor device 100 even at a lowon-voltage.

FIG. 3B is a view showing an operation state of the semiconductor devicewhen driven at a forward voltage lower than an on-voltage of theSchottky diode. Referring to FIG. 3B, when the semiconductor device 100in accordance with one embodiment of the present invention is driven ata second forward voltage lower than the on-voltage of the Schottkydiode, a depletion region DR2 generated where the second semiconductorlayer 120 and the Schottky electrode part 140 are joined together may bemore expanded than the depletion region DR1 corresponding to a casewhere the semiconductor device 100 is driven at the first forwardvoltage as described in FIG. 3A. Such the expanded depletion region DR2may be wide enough to block a current flow between the secondsemiconductor layer 124 and the Schottky electrode part 140. However,the second forward voltage may be controlled such that the depletionregion DR2 fails to be expanded to the 2DEG. Thus, in the semiconductordevice 100, a current may flow through the second current path CP2alone.

FIG. 3C is a view showing an operation state of the semiconductor devicewhen driven at a reverse voltage. Referring to FIG. 3C, when thesemiconductor device 100 is driven at the reverse voltage, a depletionregion DR3 may be more expanded to the 2DEG than the depletion regionDR2 shown in FIG. 3B. Such the depletion region DR3 allows the 2DEG tobe disconnected to thereby increase a reverse breakdown current, so thatit is possible to block all current flows passing through the first andsecond current paths CP1 and the CP2.

As described above, when the semiconductor device 100 is driven in theforward direciton, a current may flow to the second ohmic electrode 134by the first ohmic electrode 132 positioned below the Schottky electrodepart 140 even in a state where the driving voltage is lower than theon-voltage of the Schottky diode, simultaneously while the current mayflow through the first ohmic electrode 132 and the Schottky electrodepart 140 in a state where the driving voltage is higher than theon-voltage of the Schottky diode. Thus, since the semiconductor device100 may increase forward currents, it can be operated even at a lowdriving voltage. Also, when the semiconductor device 100 is driven inthe reverse direction, the depletion region DR3 generated by theSchottky electrode part 140 allows the 2DEG to be disconnected, therebystably blocking a current flow.

Hereinafter, a description will be given of a method for manufacturingthe semiconductor device in accordance with the embodiment of thepresent invention. Herein, the repeated description for thesemiconductor device will be omitted or simplified.

FIGS. 4A to 4C are views showing methods for manufacturing thesemiconductor device 100 in accordance with one embodiment of thepresent invention, respectively.

Referring to FIG. 4A, the base substrate 110 may be prepared. A step ofpreparing the base substrate 110 may include a step of preparing asemiconductor substrate. The step of preparing the base substrate 110may include a step of preparing at least one of a silicon substrate, asilicon carbide substrate, and a sapphire substrate.

The semiconductor layer 120 may be formed on the base substrate 110. Astep of forming the semiconductor layer 120 may include a step offorming the first nitride film 122 on the base substrate 110, and a stepof forming the second nitride film 124 on the first nitride film 122.For example, the step of forming the semiconductor layer 120 may beachieved by epitaxial-growing the first nitride film 122 by using thebase substrate 110 as a seed layer, and then epitaxial-growing thesecond nitride film 124 by using the epitaxial-grown first nitride film122 as a seed layer. As for an epitaxial growth process for forming thefirst and second nitride films 122 and 124, at least one of a molecularbeam epitaxial growth process, an atomic layer epitaxial growth process,a flow modulation organometallic vapor phase epitaxial growth process, aflow modulation organometallic vapor phase epitaxial growth process, anda hybrid vapor phase epitaxial growth process may be used. Furthermore,as for another process for forming the first and second nitride films122 and 124, at least one of a chemical vapor deposition process and aphysical vapor deposition process may be used.

The ohmic electrode portion 130 may be formed on the semiconductor layer120. For example, a first metal film may be formed on the second nitridefilm 124. A step of forming the first metal film may include a step offorming a metal film, which is composed of at least one of Au, Ni, Pt,Ti, Al, Pd, Ir, Rh; Co, W, Mo, Ta, Cu, and Zn, on the second nitridefilm 124 in a conformal manner. Thereafter, a step of forming a firstphotoresist pattern PR1 on the first metal film, a step of etching thefirst metal film by using the first photoresist pattern PR1 as anetching mask, and a step of removing the first photoresist pattern PR1may be sequentially performed. The step of forming the first photoresistpattern PR1 may include a step of forming a first photoresist film onthe first metal film, and then removing the first photoresist film onmiddle regions A3 such that the middle regions A3 between a centralregion A1 and edge regions A2 of the first metal film can be exposed.Thus, the first ohmic electrode 132 positioned on the central region A1and the second ohmic electrode 134 positioned on the edge regions A2 maybe formed on the second nitride film 124. The second nitride film 124 onthe middle regions A3 may be exposed. Herein, since the first ohmicelectrode 132 and the second ohmic electrode 134 are simultaneouslyformed in the same etching process, they may be formed of the samemetallic material. To this end, the first ohmic electrode 132 and thesecond ohmic electrode 134 may be formed in an in-situ scheme.Meanwhile, a process of planarizing the first metal film may be addedbefore the first metal film is etched.

Referring to FIG. 4B, a second metal film for covering all surfaces of aresultant ohmic electrode part 130 may be formed. The second metal film138 may be formed of a metallic film different from that of the ohmicelectrode part 130. Thereafter, the second photoresist pattern PR2 forexposing edge regions B1 of the second metal film 138 may be formed onthe second metal film 138. Herein, the edge regions B1 of the secondmetal film 138 may be regions including all of the edge regions A2 and apart of the middle regions A3 of the first metal film 134 of FIG. 4A.

Referring to FIG. 4C, a second photoresist pattern, indicated byreference numeral PR2 of FIG. 4B, is used as an etching mask for etchingthe second metal film 138. Thus, the Schottky electrode part 140 forentirely covering the first ohmic electrode 132 may be formed on thesecond nitride film 124. Herein, the Schottky electrode part 140 may bedisposed to be spaced apart from the second ohmic electrode 134. Thus,the region of the second nitride film 124 between the first ohmicelectrode 132 and the second ohmic electrode 134 may be exposed. Byremoving the second photoresist pattern PR2, it is possible to form thesemiconductor device 100 as shown in FIGS. 1 and 2.

Hereinafter, a description will be given of various modified examples ofthe semiconductor device in accordance with one embodiment of thepresent invention. The repeated description for the same componentsbetween the above-described semiconductor device and semiconductordevices in accordance with various modified embodiments will be omittedor simplified. Since those skilled in the art can analogize operationprocesses of the modified examples to be described from the operationstates of the semiconductor device having been described with referenceto FIGS. 3A to 3C, the description for the operation processes of themodified examples will be omitted. Also, the modified examples to bedescribed may be combined with one another and combined technologies ofthe modified examples may be enough derived from each of modifiedexamples, so detailed combined technologies will be omitted.

FIG. 5 is a plane-view showing a modified example of a semiconductordevice in accordance with one embodiment of the present invention, andFIG. 6 is a cross-sectional view taken along a line II-II′ of FIG. 5.

Referring to FIGS. 5 and 6, the semiconductor device 100 a in accordancewith one modified embodiment of the present invention may include a basesubstrate 110, a semiconductor layer 120 a, an ohmic electrode part 130,a Schottky electrode part 140 a. The semiconductor layer 120 a mayinclude the first nitride film 122 and a second nitride film 125sequentially stacked on the base substrate 110. The first nitride film122 may include a gallium nitride film, and the second nitride film 125may include an aluminium gallium nitride film. The 2DEG may be generatedon the boundary of the first and second nitride films. The ohmicelectrode part 130 may include the first ohmic electrode 132 positionedon a central region of the second nitride film 125, and second ohmicelectrode 134 having a ring shape surrounding the first ohmic electrode132 on edge regions of the second nitride film 125. The Schottkyelectrode part 140 a may be formed to entirely cover the first ohmicelectrode 132 on the central region of the second nitride film 125. Tothis end, a central portion 142 a of the Schottky electrode part 140 acovers a top surface of the first ohmic electrode 132, edge portions 144a of the Schottky electrode part 140 a may cover a part of exposed topsurfaces of the second nitride film 125 adjacent to a side surface ofthe first ohmic electrode 132, and a side surface of the first ohmicelectrode 132.

Meanwhile, the edge portions 144 a of the Schottky electrode part 140 amay be extended to inside of the second nitride film 125. For example,the edge portions 144 a may be extended downward from a top part of thesecond nitride film 124, and may be disposed to be spaced apart from thefirst nitride film 122. To this end, recesses 125 a may be provided inexposed portions of the second nitride film 125 on the middle regionsbetween the first ohmic electrode 132 and the second ohmic electrode134. The recesses 125 a may be formed to have a ring shape along thesecond nitride film 125 adjacent to a circumference of the first ohmicelectrode 132.

Herein, concentration of the 2DEG adjacent to the edge portions 144 amay be controlled by controlling depths of the edge portions 144 aprovided within the second nitride film 125. For example, the deeper thedepths of the edge portions 144 a (that is, as bottom surfaces of theedge portions 144 a become adjacent to the first nitride film 122), therelatively thinner the thickness of the second nitride film 125 adjacentto the first nitride film 122. Thus, the concentration of the 2DEGwithin the semiconductor layer 120 a adjacent to the edge portions 144 amay be reduced. On the contrary, the thinner the depths of the edgeportions 144 a (that is, as the bottom surfaces of the edge portions 144a become far from the first nitride film 122), the relatively thickerthe thickness of the second nitride film 125. In this case, theconcentration of the 2DEG within the semiconductor layer 120 a adjacentto the edge portions 144 a may be increased.

The semiconductor device 100 a in accordance with one modifiedembodiment of the present invention may include a Schottky electrodeportion 142 a having the edge portions 144 a extending to inside of thesecond nitride film 125. In this case, an on-voltage of thesemiconductor device 100 can be controlled by controlling the depths ofthe edge portions 144 a extending to inside of the semiconductor layer120 a. Thus, when the edge portions 144 a of the Schottky electrodeportion 142 a is allowed to be deep above a predetermined level, it ispossible to reduce the 2DEG of the semiconductor layer 120 adjacent tothe edge portions 144 a. Further, when the edge portions 144 a areallowed to be more deeper, it is possible to remove the 2DEG of thesemiconductor layer 120 a adjacent to the edge portions 144 a. Thesemiconductor device 100 a can reduce a reverse leakage current.

Continuously, a detailed description will be given of a method formanufacturing the semiconductor device 100 a in accordance with onemodified embodiment of the present invention. Herein, the repeateddescription for the same components between the semiconductor device 100a and the above-described semiconductor device will be omitted orsimplified.

FIGS. 7A to 7C are views showing a method for manufacturing thesemiconductor device in accordance with one modified embodiment of thepresent invention having been described with reference to FIGS. 5 and 6.

Referring to FIG. 7A, the semiconductor device 100 may be prepared. Thesemiconductor layer 120 may be formed on the base substrate 110. A stepof forming the semiconductor layer 120 may include a step of forming thefirst nitride film 122 and the second nitride film 125 on thesemiconductor layer 120 in a sequential manner.

The recesses 125 a may be formed on the second nitride film 125. Forexample, the first photoresist pattern PR1 for exposing first middleregions A3 between the central region A1 and the edge regions A2 of thesecond nitride film 125 may be formed on the second nitride film 125.Then, an etching process for removing an exposed part of the secondnitride film 125 by using the first photoresist pattern PR1 as theetching mask. Thus, the recesses 125 a may be formed on the middleregions A3 of the second nitride film 125. Herein, the concentration ofthe 2DEG of an internal region C of the semiconductor layer 120 aadjacent to the recesses 125 a can be controlled according to the depthsof the recesses 125 a. Therefore, it is possible to perform the etchingprocess in consideration of the concentration of the 2DEG of theinternal region C of the semiconductor layer 120 a adjacent to therecesses 125 a. After forming the recesses 125 a, the first photoresistpattern PR1 can be removed.

Referring to FIG. 7B, the ohmic electrode part 130 may be formed on thesecond nitride film 125. For example, a first metal film for covering aresultant second nitride film 125 may be formed, and a secondphotoresist pattern PR2 for exposing a part of the first metal film maybe formed. In this case, a part of the first metal film exposed by thesecond photoresist pattern PR2 may be the first metal film on a regionwhich further includes a part of the edge regions A2 together with themiddle regions A3. Thereafter, it is possible to perform an etchingprocess of etching the first metal film by using the second photoresistpattern PR2 as an etching mask. Thus, the first ohmic electrode 132 maybe formed on the central region A1 stimulously while the second ohmicelectrode 134 may be formed on the edge regions A2. In this case, theetching process may be controlled such that no first ohmic electrode 132can remain on the recesses 125 a. After the etching process, the secondphotoresist pattern PR2 may be removed.

Referring to FIG. 7C, the Schottky electrode part 140 a may be formed.For example, a second metal film for covering a resultant ohmicelectrode part 130 may be formed. In this case, the second metal filmmay be formed on the semiconductor layer 120 a while being buried in therecesses 125 a formed on the second nitride film 125 of thesemiconductor layer 120 a. Then, the second metal film on the edgeregions A2 may be removed. A step of removing the second metal film onthe edge regions A2 may include a step of forming a third photoresistpattern PR3 which exposes the edge regions A2 on the second metal film,and a step of etching the second metal film by using the thirdphotoresist pattern PR3 as an etching mask. Thus, the Schottky electrodepart 140 a, having a structure in which the central portion 142 a coversthe first ohmic electrode 132 and the edge portions 144 a cover the sidesurface of the second ohmic electrode 134 and the recesses 125 a, may beformed on the semiconductor layer 120 a.

FIG. 8 is a plane-view showing another modified example of thesemiconductor device in accordance with one embodiment of the presentinvention. FIG. 9 is a cross-sectional view taken along a line III-III′shown in FIG. 8.

Referring to FIGS. 8 and 9, the semiconductor device 100 b in accordancewith another modified embodiment of the present invention may includethe base substrate 110, a semiconductor layer 120 b, an ohmic electrodepart 130 b, and the Schottky electrode part 140.

The semiconductor layer 120 b may include a first nitride film 123 and asecond nitride film 126 sequentially stacked on the semiconductor device100. A 2DEG may be generated on a boundary between the first and secondnitride films. The ohmic electrode part 130 b may include a first ohmicelectrode 132 b, and second ohmic electrode 134 b, wherein the firstohmic electrode 132 b is disposed on the central region of the secondnitride film 126, and the second ohmic electrode 134 b having a ringshape surrounding the first ohmic electrode 132 b on the edge regions ofthe second nitride film 126. Then, the Schottky electrode part 140 maybe formed to entirely cover the first ohmic electrode 132 b on thecentral region of the semiconductor layer 120 b. For example, thecentral portion 142 of the Schottky electrode part 140 may cover the topsurface of the first ohmic electrode 132 b, and the edge portions 144 ofthe Schottky electrode part 140 may cover the side surface of the firstohmic electrode 132 b and the top surface of the second nitride film 124adjacent thereto. In this case, the edge portions 144 of the Schottkyelectrode part 140 may be disposed to be spaced apart from the secondohmic electrode 134 b.

Meanwhile, the ohmic electrode part 130 b may be extended to inside ofthe semiconductor layer 120 b. For example, the first ohmic electrode132 b and the second ohmic electrode 134 b may be extended to the insideof the first nitride film 123 through the second nitride film 126. Inthis case, the first ohmic electrode 132 b and the second ohmicelectrode 134 b may be formed to pass through a location of the 2DEG. Tothis end, the semiconductor layer 120 b may have first and second recess127 and 128 formed therewithin for burring the first ohmic electrode 132b and second ohmic electrode 134 b inside of the semiconductor layer 120b.

The first recesses 127 may be a trench in which the first ohmicelectrode 132 b is buried, and the second recess 128 may be a trench inwhich the second ohmic electrode 134 b is buried. Although the presentembodiment has been illustrated taking an example where the firstrecesses 127 has the same depth as that of the second recess 128, depthsof the first and second recess 127 and 128 may be selectively differedfrom each other. In the semiconductor device 100 b, a current may flowonly in a horizontal direction between the first ohmic electrode 132 band the second ohmic electrode 134 b.

The semiconductor device 100 b having the above-described structure cancontrol the concentration of the 2DEG generated on the semiconductorlayer 120 b by controlling a depth at which the ohmic electrode part 130b is formed inside of the semiconductor layer 120 b.

Continuously, a detailed description will be given of a method formanufacturing the semiconductor device 100 b in accordance with anothermodified embodiment of the present invention. FIGS. 10A to 10C are viewsshowing a method for manufacturing the semiconductor device 100 b havingbeen described with reference to FIGS. 8 and 9.

Referring to FIG. 10, the base substrate 110 may be prepared, and thefirst nitride film 123 and the second nitride film 126 may besequentially formed on the base substrate 110. The first nitride film123 may include a gallium nitride film, and the second nitride film 126may include an aluminium gallium nitride film. The first recesses 127and the second recess 128 may be formed on the second nitride film 126.For example, it is possible to perform an etching process for etchingthe semiconductor layer 120 b by using the resultant PR1 as an etchingmask after the first photoresist pattern PR1 exposing the central regionA1 and the edge regions A2 of the semiconductor layer 120 b is formed onthe second nitride film 126. For example, in the etching process, depthsof the first recesses 127 and the second recess 128 pass through thesecond nitride film 126 such that the depths can be controlled to beextended to the inside of the first nitride film 123. After the etchingprocess is performed, the first photoresist pattern PR1 may be removed.Herein, the concentration of the 2DEG of the internal region C of thesemiconductor layer 120 b adjacent to the first and second recess 127and 128 can be controlled according to the depths of the first andsecond recess 127 and 128. Therefore, it is possible to perform theetching process in consideration of the concentration of the 2DEG in theinternal region C of the semiconductor layer 120 b adjacent to the firstand second recess 127 and 128.

Referring to FIG. 10B, it is possible to form the ohmic electrode part130 b. For example, it is possible to form a first metal film whichcovers a resultant second nitride film 126 having the first and secondrecess 127 and 128. Herein, the first metal film may be formed whilebeing burred in the first and second recess 127 and 128. It is possibleto form the second photoresist pattern PR2, which exposes the firstmetal film on the middle region A3 between the central region A1 and theedge regions A2, on the first metal film. It is possible to etch thefirst metal film by using the second photoresist pattern PR2 as theetching mask. Thus, the first ohmic electrode 132 b may be formed on thecentral region A1 of the semiconductor layer 120 b, and the second ohmicelectrode 134 b may be formed on the edge regions A2 of thesemiconductor layer 120 b.

Referring to FIG. 10C, it is possible to form the Schottky electrodepart 140. For example, the second metal film may be formed on aresultant ohmic electrode part 130 b. The second metal film may be afilm composed of a metallic material different from that of the firstmetal film, for formation of the ohmic electrode part 130 b. A thirdphotoresist pattern PR3 which exposes a part of the edge regions A2 andthe middle region A3 may be formed on the second metal film, and thesecond metal film may be etched by using the resultant third photoresistpattern PR3 as the etching mask. Thus, the Schottky electrode part 140,which entirely covers the first ohmic electrode 132 b, may be formed onthe central region A1 of the semiconductor layer 120.

FIG. 11 is a plane-view showing another modified example of thesemiconductor device in accordance with an embodiment of the presentinvention. FIG. 12 is a cross-sectional view taken along a line IV-IV′shown in FIG. 11.

Referring to FIGS. 11 and 12, the semiconductor device 100 c inaccordance with another modified embodiment of the present invention mayinclude a base substrate 110, a semiconductor layer 120, an ohmicelectrode part 130, a Schottky electrode part 142, and a field plate150. The semiconductor layer 120 may include a first nitride film 122and a second nitride film 124 sequentially stacked on the base substrate110. A 2DEG may be generated on a boundary of the first and secondnitride films. The ohmic electrode part 130 may include a first ohmicelectrode 132 and second ohmic electrode 134. The first ohmic electrode132 may be disposed on a central region of the second nitride film 124.The second ohmic electrode 134 has with a ring shape surrounding thefirst ohmic electrode 132 on the edge regions of the second nitride film124. The Schottky electrode part 142 may be formed to entirely cover thefirst ohmic electrode 132 on the central region of the second nitridefilm 124. To this end, a central portion 142 of the Schottky electrodepart 140 covers a top surface of the first ohmic electrode 132, edgeportions 144 of the Schottky electrode part 140 may cover a side surfaceof the first ohmic electrode 132 and a part of exposed top surfaces ofthe second nitride film 124 adjacent thereto.

Meanwhile, the field plate 150 may be disposed on the semiconductorlayer 120 between the second ohmic electrode 134 and the Schottkyelectrode part 142. In this case, external side portion 152 of the fieldplate 150 may be provided to be partially covered by the second ohmicelectrode 134, and an internal side portion 154 of the field plate 150may be provided to be partially covered by the edge portions 144 a ofthe Schottky electrode part 140. The field plate 150 can provide aneffect of distributing an electric field concentrated on a cornerportion of the Schottky electrode part 142 and the ohmic electrode part130.

Continuously, a detailed description will be given of a method formanufacturing a semiconductor device 100 c in accordance with anothermodified embodiment of the present invention. FIGS. 13A to 13C are viewsshowing methods for manufacturing a semiconductor device 100 c havingbeen described with reference to FIGS. 11 and 12, respectively.

Referring to FIG. 13A, the base substrate 110 may be prepared, and thefirst nitride film 122 and the second nitride film 124 may besequentially formed on the base substrate 110. The first nitride film122 may include a gallium nitride, and the second nitride film 124 mayinclude an aluminium gallium nitride.

The field plate 150 may be formed. A step of forming the field plate 150may include a step of forming an insulating film on the second nitridefilm 124 in a conformal manner, a step of forming the first photoresistpattern PR1 which exposes a central region and edge regions of theinsulating film, on the insulating film, and a step of etching theinsulating film by using the first photoresist pattern PR1 as an etchingmask. Thus, the field plate 150 disposed between the central region andthe edge regions of the semiconductor layer 120 may be formed on thesemiconductor layer 120. After the field plate 150 is formed, the firstphotoresist pattern PR1 may be removed.

Referring to FIG. 13B, the ohmic electrode part 130 may be formed. Forexample, the first metal film may be formed that entirely covers aresultant field plate 150. Then, the second photoresist pattern PR2 maybe formed on the first metal film. The second photoresist pattern PR2can expose the first metal film on the middle regions A3 between thecentral region A1 and the edge regions A2. In addition, the secondphotoresist pattern PR2 may be provided such that the first metal filmon the external side portion 152 of the field plate 150 fails to beexposed. Thereafter, it is possible to etch the first metal film byusing the second photoresist pattern PR2 as an etching mask. Thus, thefirst ohmic electrode 132 may be formed on the central region A1 of thesemiconductor layer 120, and the second ohmic electrode 134 may beformed on the edge regions A2 of the semiconductor layer 120. Herein,the second ohmic electrode 134 may be formed to partially cover theexternal side portion 152 of the field plate 150. In this case, it ispossible to distribute an electric field concentrated on the cornerportion of the second ohmic electrode 134 which comes into contact withthe field plate 150.

Referring to FIG. 13C, the Schottky electrode part 140 may be formed.For example, the second metal film may be formed on the resultant ohmicelectrode part 130. The second metal film may be a film of a metallicmaterial different from that of the first metal film, for formation ofthe ohmic electrode part 130. It is possible to form the thirdphotoresist pattern PR3 which exposes a part of the edge regions A2 andthe middle regions A3 on the second metal film. In addition, the thirdphotoresist pattern PR3 may be provided such that the second metal filmon the internal side portion 154 of the field plate 150 fails to beexposed. Thereafter, it is possible to etch the second metal film byusing the third photoresist pattern PR3 as an etching mask. Thus, it ispossible to form the Schottky electrode part 142 which entirely coversthe first ohmic electrode 132 b on the central region A1 of thesemiconductor layer 120. Herein, the Schottky electrode part 142 may beformed to partially cover the internal side portion 154 of the externalside portion 152. In this case, it is possible to distribute an electricfield concentrated on an edge portion of the Schottky electrode part 140which comes into contact with the field plate 150.

Hereinafter, a detailed description will be given of a method formanufacturing the semiconductor device in accordance with otherembodiments of the present invention with referent to accompanyingdrawings.

FIG. 14 is a view showing a semiconductor device in accordance withother embodiments of the present invention, and FIG. 15 is across-sectional view taken along a line V-V′ of FIG. 14.

Referring to FIGS. 14 and 15, a semiconductor device 200 in accordancewith other embodiment of the present invention may include a basesubstrate 210, a semiconductor layer 220, an ohmic electrode part 230,and a Schottky electrode part 240.

The base substrate 210 may be a plate for formation of the semiconductordevice having the Schottky diode structure. For example, the basesubstrate 210 may be a semiconductor substrate. The base substrate 210may correspond to at least one of a silicon substrate, a silicon carbidesubstrate, and a sapphire substrate.

The semiconductor layer 220 may be disposed on the base substrate 210.For example, the semiconductor layer 220 may include a first nitridefilm 222 and a second nitride film 224 which are sequentially stacked onthe base substrate 210. The second nitride film 224 may be formed of amaterial having an energy band gap wider than that of the first nitridefilm 222. In addition, the second nitride film 224 may be formed of amaterial having a lattice parameter different from that of the firstnitride film 222. For example, the first nitride film 222 and the secondnitride film 224 may be films which contain a III-nitride-basedmaterial. In particular, the first nitride film 222 and the secondnitride film 224 may be formed of any one of GaN, AlGaN, InGaN, andInAlGaN. For example, the first nitride film 222 may be a galliumnitride film, and the second nitride film 224 may be an aluminiumgallium nitride film. Herein, the first nitride film 222 of thesemiconductor layer 220 is formed of P-type GaN having high resistivity,thereby reducing a leakage current of the semiconductor device 200.

The semiconductor layer 220 may be provided with 2-Dimensional ElectronGas (2DEG) on a boundary of the first nitride film 222 and the secondnitride film 224. When the semiconductor device 200 is operated, acurrent flows through the 2DEG. Meanwhile, a buffering film (not shown)may be further formed between the base substrate 210 and the firstnitride film 222 so as to solve problems caused by lattice mismatchbetween the base substrate 210 and the first nitride film 222.

The ohmic electrode part 230 may be disposed on the second nitride film224. For example, the ohmic electrode part 230 may include first ohmicelectrodes 232 and a second ohmic electrode 234. The first ohmicelectrodes 232 may be disposed on a central region A1 of the secondnitride film 224. Each of the first ohmic electrodes 232 may have aisland-shaped cross section. For example, each of the first ohmicelectrodes 232 may have a rectangular-shaped cross section. The firstohmic electrodes 232 may be disposed to be spaced apart from one anotherat a predetermined space. The first ohmic electrodes 232 may be disposedto be in a grid configuration on the central region A1.

The second ohmic electrode 234 may be formed along the edge regions A2of the second nitride film 224. The second ohmic electrode 234 may bedisposed on edge regions A2 of the second nitride film 224 to surroundthe first ohmic electrodes 232. Thus, the second ohmic electrode 234 maybe mainly formed in a ring shape. Also, the second ohmic electrode 234may be disposed to be spaced apart from the first ohmic electrodes 232at a predetermined space.

The Schottky electrode part 240 may be provided to cover the first ohmicelectrodes 232. For example, the Schottky electrode part 240 may beprovided on the central region A1 of the second nitride film 224 so thatit can entirely cover the first ohmic electrodes 232. Thus, the Schottkyelectrode part 240 and the first ohmic electrodes 232 have a prominenceand depression structure in which they are engaged with each other upand down. The Schottky electrode part 240 may have a first bondingportions 242 bonded to the first ohmic electrodes 232, and a secondbonding portion 244 bonded to a top surface of the semiconductor layer220 adjacent to the first ohmic electrodes 232.

In the semiconductor device 200 having the above-described structure,each of the first ohmic electrodes 232 may be bonded to the secondnitride film 224 on the central region A1 to thereby achieve an ohmiccontact, the second ohmic electrode 234 may be bonded to the secondnitride film 224 on the central region A1 to thereby achieve an ohmiccontact. The Schottky electrode part 240 may be bonded to the firstohmic electrodes 232 and the second nitride film 224 on the centralregion A1 to thereby achieve an ohmic contact. Also, the Schottkyelectrode part 240 may be used as an anode electrode, and the secondohmic electrode 234 may be used as a cathode electrode.

Meanwhile, the ohmic electrode part 230 and the Schottky electrode part240 may be formed of various materials. For example, the first ohmicelectrodes 232 and the second ohmic electrode 234 may be formed of thesame metallic material, and the Schottky electrode part 240 may beformed of a metallic material different from that of the first andsecond ohmic electrodes 232 and 234. For example, the first and secondohmic electrodes 232 and 234 may be formed of a metallic materialcomposed of at least one of Al, Mo, Au, Ni, Pt, Ti, Pd, Ir, Rh, Co, W,Ta, Cu, Zn. On the contrary, the Schottky electrode part 240 may beformed of a material composed of one or more metal elements differentfrom those of the ohmic electrode part 230.

Continuously, a detailed description will be given of various operationstates of the semiconductor device 200 in, accordance with an embodimentof the present invention with reference to FIGS. 14 and 15.

FIGS. 16A to 16C are views showing operation states of the semiconductordevice shown in FIG. 15, respectively. FIG. 16A is a view showing anoperation state of the semiconductor device when driven at a forwardvoltage equal to or higher than an on-voltage of the Schottky diode.Referring to FIG. 16A, when the semiconductor device 200 in accordancewith another embodiment of the present invention is driven at a firstforward voltage equal to or higher than the on-voltage of the Schottkydiode, a depletion region (DR1) generated where the second semiconductorlayer 220 and the Schottky electrode part 240 are joined together may berelatively reduced. Thus, a current may flow through a first currentpath CP1 and a second current path CP2, wherein the first current pathCP1 passes through the 2DEG from the first ohmic electrodes 232, and thesecond current path CP2 passes through the 2DEG from the Schottkyelectrode part 240. In this case, since forward currents of thesemiconductor device 200 is increased, it is possible to operate thesemiconductor device 200 even at a low on-voltage.

FIG. 16B is a view showing an operation state of the semiconductordevice when driven at a forward voltage lower than an on-voltage of theSchottky diode. Referring to FIG. 16B, when the semiconductor device 200in accordance with one embodiment of the present invention is driven ata second forward voltage lower than the on-voltage the Schottky diode, adepletion region DR2 generated where the second semiconductor layer 220and the Schottky electrode part 240 are joined together may be moreexpanded than the depletion region DR1 corresponding to a case where thesemiconductor device 200 is driven at the first forward voltage asdescribed in FIG. 16A. Such the expanded DR2 may be wide enough to blocka current flow between the second nitride film 224 and the Schottkyelectrode part 240. However, the second forward voltage may becontrolled such that the depletion region DR2 fails to be expanded tothe 2DEG. Thus, in the semiconductor device 200, a current may flowthrough the second current path CP2 alone.

FIG. 16C is a view showing an operation state of the semiconductordevice when driven at a reverse voltage. Referring to FIG. 16C, when thesemiconductor device 200 is driven at the reverse voltage, a depletionregion DR3 may be more expanded to the 2DEG than the depletion regionDR2 shown in FIG. 16B. The depletion region DR3 allows the 2DEG to bedisconnected, thereby blocking all current flows passing through thefirst current path CP1 and the second current path CP2.

As described above, when the semiconductor device 200 is driven in theforward direction, a current may flow by the first ohmic electrodes 232positioned below the Schottky electrode part 240 even in a state wherethe driving voltage is lower than the on-voltage of the Schottky diode,simultaneously while the current may flow through the first ohmicelectrodes 232 and the Schottky electrode part 240 in a state where thedriving voltage is higher than the on-voltage of the Schottky diode.Thus, since the semiconductor device 200 may increase forward currents,it can be operated even at a low driving voltage. Also, when thesemiconductor device 200 is driven in the reverse direction, it ispossible to stably block a current flow by disconnecting the 2DEGthrough the depletion region DR3 which is generated by the Schottkyelectrode part 240.

Hereinafter, a description will be given of a method for manufacturingthe semiconductor device in accordance with other embodiment of thepresent invention. Herein, the repeated description for thesemiconductor device will be omitted or simplified.

FIGS. 17A to 17C are views showing methods for manufacturing thesemiconductor device in accordance with one embodiment of the presentinvention, respectively.

Referring to FIG. 17A, the base substrate 210 may be prepared. A step ofpreparing the base substrate 210 may include a step of preparing asemiconductor substrate. The step of preparing the base substrate 210may include a step of preparing at least one of a silicon substrate, asilicon carbide substrate, and a sapphire substrate.

The semiconductor layer 220 may be formed on the base substrate 210. Astep of forming the semiconductor layer 220 may include a step offorming the first nitride film 222 on the base substrate 210, and a stepof forming the second nitride film 224 on the first nitride film 222.For example, the step of forming the semiconductor layer 220 may beachieved by epitaxial-growing the first nitride film 222 by using thebase substrate 210 as a seed layer, and then epitaxial-growing thesecond nitride film 224 by using the epitaxial-grown first nitride film222 as a seed layer. As for an epitaxial growth process for forming thefirst and second nitride films 222 and 224, at least one of a molecularbeam epitaxial growth process, an atomic layer epitaxial growth process,a flow modulation organometallic vapor phase epitaxial growth process, aflow modulation organometallic vapor phase epitaxial growth process, anda hybrid vapor phase epitaxial growth process may be used. Furthermore,as for another process for forming the first and second nitride films222 and 224, at least one of a chemical vapor deposition process and aphysical vapor deposition process may be used.

The ohmic electrode part 230 may be formed on the semiconductor layer220. For example, a first metal film may be formed on the second nitridefilm 224. A step of forming the first metal film may include a step offorming a metal film, which is composed of at least one of Au, Ni, Pt,Ti, Al, Pd, Ir, Rh, Co, W, Mo, Ta, Cu, and Zn, on the second nitridefilm 224 in a conformal manner. Thereafter, a first photoresist patternPR1 may be formed on the first metal film. The step of forming the firstphotoresist pattern PR1 may include a step of forming the firstphotoresist pattern PR1 on the first metal film, and then removing apart of the first photoresist pattern PR1 so that the first metal filmon a region, excluding the edge regions A2 and regions where the firstohmic electrodes 232 shown in FIG. 17 are to be formed, can be exposed.Then, it is possible to remove the first photoresist pattern PR1 afteretching the first metal film by using the first photoresist pattern PR1as an etching mask. Thus, a plurality of first ohmic electrodes 232disposed to be in a lattice configuration on the central region A1 andthe second ohmic electrode 234 having the ring-shape formed along theedge regions A2 may be formed on the second nitride film 224. Herein,since the first ohmic electrodes 232 and the second ohmic electrode 234are simultaneously formed in the same etching process, they may beformed of the same metallic material. For example, the first ohmicelectrodes 232 and the second ohmic electrode 234 may be formed in anin-situ scheme at the same time. Meanwhile, a process of planarizing thefirst metal film may be added before the first metal film is etched.

Referring to FIG. 17B, a second metal film 238 for covering all surfacesof the resultant ohmic electrode part 230 may be formed. The secondmetal film 238 may be formed of a metallic film different from that ofthe ohmic electrode part 230. Thereafter, the second photoresist patternPR2 for exposing edge regions B of the second metal film 238 may beformed on the second metal film 238. Herein, the edge regions B of thesecond metal film 238 may be a region including a part of the middleregions A3 and all of the edge regions A2 of the second ohmic electrode234 of FIG. 17A.

Referring to FIG. 17C, a second photoresist pattern indicated byreference numeral PR2 of FIG. 17B is used as an etching mask for etchingthe second metal film 238. Thus, the Schottky electrode part 240 forentirely covering the first ohmic electrodes 232 may be formed on thesecond nitride film 224. Therefore, the Schottky electrode part 240 andthe first ohmic electrodes 232 are configured to be in prominence anddepression structure, in which they are engaged with each other, on thecentral region A1 up and down. Herein, the Schottky electrode part 240may be disposed to be spaced apart from the second ohmic electrode 234.Thus, the region of the second nitride film 224 between the first ohmicelectrodes 232 and the second ohmic electrode 234 may be exposed. Byremoving the second photoresist pattern PR2, it is possible to form thesemiconductor device 200 as shown in FIGS. 15 and 16.

Hereinafter, a description will be given of various modified examples ofthe semiconductor device in accordance with other embodiment of thepresent invention. The repeated description for the same componentsbetween the above-described semiconductor device and semiconductordevices in accordance with various modified embodiments will be omittedor simplified. Since those skilled in the art can analogize operationprocesses of the modified examples to be described from the operationstates of the semiconductor device having been described with referenceto FIGS. 16A to 16C, the description for operation processes of themodified examples will be omitted.

FIG. 18 is a plane-view showing a modified example of a semiconductordevice in accordance with other embodiment of the present invention, andFIG. 19 is a cross-sectional view taken along a line VI-VI″ of FIG. 18.

Referring to FIGS. 18 and 19, the semiconductor device 200 a inaccordance with one modified embodiment of the present invention mayinclude a base substrate 210, a semiconductor layer 220 a, an ohmicelectrode part 230, a Schottky electrode part 240 a. The semiconductorlayer 220 a may include the first nitride film 222 and a second nitridefilm 225 sequentially stacked on the base substrate 210. The firstnitride film 222 may be formed of GaN, and the second nitride film 225may be formed of AlGaN. A 2DEG may be generated on a boundary of thefirst and second nitride films. The ohmic electrode part 230 may includea plurality of first ohmic electrodes 232, and a second ohmic electrode234, wherein the first ohmic electrodes have an island-shaped crosssection on a central region of the second nitride film 225, and thesecond ohmic electrode has a ring shape formed along edge regions of thesecond nitride film 225. The Schottky electrode part 240 a may be formedto entirely cover the first ohmic electrodes 232 on the central regionA1 of the second nitride film 225. The Schottky electrode part 240 a mayhave first bonding portions 242 a bonded to the first ohmic electrodes232, and a second bonding portion 244 a bonded to the semiconductorlayer 220 adjacent to the first ohmic electrodes 232.

Meanwhile, the second bonding portion 244 a of the Schottky electrodepart 240 a may be extended to inside of the second nitride film 224. Forexample, the second bonding portion 244 a may be extended downward froma top part of the second nitride film 225, and may be disposed to bespaced apart from the first nitride film 222. To this end, recesses 225a may be provided in exposed portions of the second nitride film 225 onthe middle regions between the first ohmic electrodes 232 and the secondohmic electrode 234. The recesses 225 a may be formed within a region ofthe second nitride film 225 adjacent to the first ohmic electrodes 232.

Herein, concentration of the 2DEG adjacent to the second bonding portion244 a may be controlled by controlling depth of the second bondingportion 244 a provided within the second nitride film 225. For example,the deeper the depth of the second bonding portion 244 a (that is, as abottom surface of the second bonding portion 244 a becomes adjacent tothe first nitride film 222), the relatively thinner the thickness of thesecond nitride film 225 adjacent to the first nitride film 222. Thus,the concentration of the 2DEG within the semiconductor layer 220 aadjacent to the edge portions 244 a may be reduced. On the contrary, thethinner the depth of the second bonding portion 244 a (that is, as thebottom surface of the second bonding portion 244 a becomes far from thefirst nitride film 222), the relatively thicker the thickness of thesecond nitride film 225. In this case, the concentration of the 2DEG ofan internal region C of the semiconductor layer 220 a adjacent to thesecond bonding portion 244 a may be increased.

The semiconductor device 200 a in accordance with one modifiedembodiment of the present invention may include the Schottky electrodepart 240 a having the second bonding portion 244 a extending to insideof the second nitride film 225. In this case, an on-voltage of thesemiconductor device 200 can be controlled by controlling the depth ofthe second bonding portion 244 a extending to inside of thesemiconductor layer 220 a. For example, when the second bonding portion244 a of the Schottky electrode part 240 a are allowed to be deep abovea predetermined level, it is possible to reduce the 2DEG of C region ofthe semiconductor layer 220 adjacent to the second bonding portion 244a. Further, when the second bonding portion 244 a is allowed to bedeeper, it is possible to remove the 2DEG of C region of thesemiconductor layer 220 a adjacent to the edge portions 244 a. Thesemiconductor device 200 a can reduce a reverse leakage current.

Continuously, a detailed description will be given of a method formanufacturing the semiconductor device 200 a in accordance with onemodified embodiment of the present invention. Herein, the repeateddescription for the semiconductor device 200 a will be omitted orsimplified.

FIGS. 20A to 20C are views showing methods for manufacturing thesemiconductor device in accordance with one modified embodiment of thepresent invention having been described with reference to FIGS. 18 and19, respectively.

Referring to FIG. 20A, the base substrate 110 may be prepared. Thesemiconductor layer 220 may be formed on the base substrate 210. Thestep of forming the semiconductor layer 220 may include a step offorming the first nitride film 222 and the second nitride film 225 onthe base substrate 210 in a sequential manner. For example, a step offorming the first nitride film 222 may include a step of growing a GaNfilm on the base substrate 210 by using the base substrate 210 as a seedlayer, and a step of forming the second nitride film 225 includes a stepof growing an AlGaN film on the first nitride film 222 by using thefirst nitride film 222 as a seed layer.

The ohmic electrode part 230 may be formed on the second nitride film225. For example, a first metal film which covers all surfaces of theresultant second nitride film 225 may be formed, and the firstphotoresist pattern PR1 which partially exposes the first metal film maybe formed. The first photoresist pattern PR1 can expose a region (d)excluding a lattice-shaped region where the middle regions A3 of thesemiconductor layer 220 and the first ohmic electrodes 232 are to beformed. Thereafter, it is possible to perform an etching process of thefirst metal film by using the first photoresist pattern PR1 as anetching mask. Thus, a plurality of the first ohmic electrodes 232disposed to be in a lattice configuration may be formed on the centralregion A1 simultaneously while the ring-shaped second ohmic electrode234 may be formed on the edge regions A2. For example, the first ohmicelectrodes 232 and the second ohmic electrode 234 may be formed in anin-situ scheme. The first photoresist pattern PR1 may be removed afterthe etching process is performed.

Referring to FIG. 20B, the recesses 225 a may be formed within thesecond nitride film 225. For example, the second photoresist pattern PR2which exposes a part of the middle regions A3 may be formed on thesecond nitride film 225. The part of the middle regions A3 may be aregion spaced apart from the edge regions A2 from among electrodesdisposed on the outermost of the first ohmic electrodes 232. It ispossible to perform an etching process which removes an exposed part ofthe second nitride film 225 by using the second photoresist pattern PR2as an etching mask. Thus, the recesses 225 a may be formed on the middleregions A3 of the second nitride film 225. Herein, the concentration ofthe 2DEG of an internal region C of the semiconductor layer 220 aadjacent to the recesses 225 a can be controlled according to on thedepths of the recesses 225 a. Therefore, it is possible to perform theetching process in consideration of the concentration of the 2DEG of theinternal region C of the semiconductor layer 220 a adjacent to therecesses 225 a. After the recesses 225 a are formed, the firstphotoresist pattern PR1 can be removed.

Referring to FIG. 20C, the Schottky electrode part 240 a may be formed.For example, a second metal film for covering the resultant ohmicelectrode part 230 may be formed. In this case, the second metal filmmay be formed to cover entirely the semiconductor layer 220 a whilebeing buried in the recesses 225 a formed on the second nitride film 225of the semiconductor layer 220 a. Then, the second metal film on theedge regions A2 may be removed. For example, a step of forming a thirdphotoresist pattern PR3, which exposes the edge regions A2 and a partialregion B of the middle regions A3, on the second metal film, and a stepof etching the second metal film by using the third photoresist patternPR3 as an etching mask may be included. Thus, on the semiconductor layer220 a, the Schottky electrode part 240 a may be formed that entirelycovers the first ohmic electrodes 232 and the second bonding portion 244a is extended to inside of the second nitride film 224. Thus, theSchottky electrode part 240 a is engaged with the first ohmic electrodes232 to thereby have a prominence and depression structure up and down.

FIG. 21 is a plane-view showing another modified example of thesemiconductor device in accordance with one embodiment of the presentinvention. FIG. 22 is a cross-sectional view taken along a line VII-VII′shown in FIG. 21.

Referring to FIGS. 21 and 22, the semiconductor device 200 b inaccordance with another modified embodiment of the present invention mayinclude the base substrate 210, a semiconductor layer 220 b, an ohmicelectrode part 230 b, and the Schottky electrode part 240. Thesemiconductor layer 220 b may include a first nitride film 223 and asecond nitride film 126 sequentially stacked on the base substrate 210.A 2DEG may be generated on a boundary between the first and secondnitride films. The ohmic electrode part 230 b may include a plurality offirst ohmic electrodes 232 b, and a second ohmic electrode 234 b,wherein the first ohmic electrodes 232 b are formed to have anisland-shaped cross section on the central region of the second nitridefilm 226, and the second ohmic electrode 234 b has a ring shape formedalong an edge region of the second nitride film 226. Then, the Schottkyelectrode part 240 may be formed to entirely cover the first ohmicelectrodes 232 b on the central region of the semiconductor layer 220 b.The Schottky electrode part 240 may include the first bonding portions242 bonded to the first ohmic electrodes 232 b, and the second bondingportion 244 bonded to the semiconductor layer 220 b adjacent to thefirst ohmic electrodes 232 b. Thus, the edge portion of the Schottkyelectrode part 240 may be disposed to be spaced apart from the secondohmic electrode 234 b.

Meanwhile, the ohmic electrode part 230 b may be extended to the insideof the semiconductor layer 220 b. For example, the first ohmicelectrodes 232 b and the second ohmic electrode 234 b may be formed tobe extended to the inside of the second semiconductor layer 226, and maybe formed to be spaced apart from the first semiconductor layer 223. Tothis end, the semiconductor layer 220 b may have first and second recess227 and 228 formed thereon. The first recesses 227 may be trenches inwhich the first ohmic electrodes 232 b are buried, and the second recess228 may be trenches in which the second ohmic electrode 234 b is buried.Although the present embodiment has been illustrated taking an examplewhere the first recesses 227 have the same depths as those of the secondrecess 228, depths of the first and second recess 227 and 228 may beselectively differed from each other.

The semiconductor device 200 b can control the concentration of the 2DEGgenerated on the semiconductor layer 220 b by controlling the depth atwhich the ohmic electrode part 230 b is formed inside of thesemiconductor layer 220 b.

FIG. 23 is a view showing another modified example of a semiconductordevice shown in FIG. 22. Referring to FIG. 23, a semiconductor device200 b′ may have a structure in which the first ohmic electrodes 232 band 234 b are extended to the inside of the first nitride film 223, incomparison with the semiconductor device 200 b having been describedwith reference to FIGS. 21 and 22. For example, the first ohmicelectrodes 232 b and the second ohmic electrode 234 b pass through thesecond semiconductor layer 226 in such a manner to be extended to theinside of the first semiconductor layer 223. In this case, the firstohmic electrodes 232 b and the second ohmic electrode 234 b may beformed to pass through a location of the 2DEG. To this end, thesemiconductor layer 220 b may have first and second recess 227 a and 228a formed thereon. The first recesses 227 a may be trenches in which thefirst ohmic electrodes 232 b are buried, and the second recess 228 a maybe trench in which the second ohmic electrode 234 b is buried. Althoughthe present embodiment has been illustrated taking an example where thefirst recesses 227 a has the same depth as that of the second recess 228a, depths of the first and second recess 227 a and 228 a may beselectively differed from each other. In the semiconductor device 200b′, a current may flow only in a horizontal direction between the firstohmic electrodes 232 b and the second ohmic electrode 234 b.

Continuously, a detailed description will be given of a method formanufacturing the semiconductor device 200 b in accordance with anothermodified embodiment of the present invention. FIGS. 24A to 24C are viewsshowing a method for manufacturing the semiconductor device 200 b havingbeen described with reference to FIGS. 21 and 22.

Referring to FIG. 24A, the base substrate 110 is prepared, and the firstnitride film 223 and the second nitride film 226 may be sequentiallyformed on the base substrate 210. The first nitride film 223 may includeGaN, and the second nitride film 226 may include AlGaN. The firstrecesses 227 and the second recess 228 may be formed on the secondnitride film 226. For example, the first photoresist pattern PR1 may beformed on the second nitride film 226. The first photoresist pattern PR1can expose a partial region C of the central region A1 and the edgeregions A2 of the semiconductor layer 220 b. In this case, the partialregion C of the central region A1 may be a region where the first ohmicelectrodes, indicated by reference numeral 232 of FIG. 24B, are to beformed. It is possible to perform an etching process for etching thesemiconductor layer 220 b by using the resultant PR1 as an etching mask.For example, in the etching process, depths of the first recesses 227and the second recess 228 are extended to inside of the second nitridefilm 226, and they can be controlled to be spaced apart from the firstnitride film 223. When the etching process is performed, the firstphotoresist pattern PR1 may be removed. Herein, the concentration of the2DEG of the internal region C of the semiconductor layer 220 b adjacentto the first and second recess 227 and 228 can be controlled based onthe depths of the first and second recess 227 and 228. Therefore, it ispossible to perform the etching process in consideration of theconcentration of the 2DEG in the internal region C of the semiconductorlayer 220 b adjacent to the first and second recess 227 and 228.

Referring to FIG. 24B, it is possible to form the ohmic electrode part230 b. For example, it is possible to form a first metal film whichcovers all surfaces of resultant second nitride film 226 having thefirst and second recess 227 and 228. Herein, the first metal film may beformed while burring the first and second recess 227 and 228. It ispossible to etch the first metal film by using the second photoresistpattern PR2 as the etching mask, after forming the second photoresistpattern PR2 which exposes the first metal film on the regions excludingregions where the first recesses 227 and 228 are formed. Thus, aplurality of the first ohmic electrodes 232 b having island-shaped crosssections may be formed in a lattice configuration on the central regionA1 of the semiconductor layer 220 b, and the second ohmic electrode 234b having a ring shape may be formed on the edge regions A2 of thesemiconductor layer 220 b.

Referring to FIG. 24C, it is possible to form the Schottky electrodepart 240. For example, the second metal film may be formed on aresultant ohmic electrode part 230 b. The second metal film may be afilm composed of a metallic material different from that of the firstmetal film for formation of the ohmic electrode part 230 b. It ispossible to form a PR3, exposing a region B1 including a part of theedge regions A2 and the middle regions A3 on the second metal film, onthe second metal film, and to etch the second metal film by using thethird photoresist pattern PR3 as an etching mask. Thus, the Schottkyelectrode part 240 a entirely covers the first ohmic electrodes 232 b onthe central region A1 of the semiconductor layer 220, thereby to have aprominence and depression structure.

FIG. 25 is a view showing another modified example of the semiconductordevice in accordance with other embodiment of the present invention.FIG. 26 is a cross-sectional view taken along a line VIII-VIII′ shown inFIG. 25.

Referring to FIGS. 25 and 26, the semiconductor device 200 c inaccordance with another modified embodiment of the present invention mayinclude a base substrate 210, a semiconductor layer 220, an ohmicelectrode part 230, a Schottky electrode part 240, and a field plate250. The semiconductor layer 220 may include the first nitride film 222and the second nitride film 224 sequentially stacked on the basesubstrate 210. The 2DEG may be generated on the boundary of the firstand second nitride films. The ohmic electrode part 230 may include aplurality of first ohmic electrodes 232 and second ohmic electrode 234.The first ohmic electrodes 232 may be disposed on a central region ofthe second nitride film 224 and have island-shape cross sections. Thesecond ohmic electrode 234 may have a ring shape surrounding the firstohmic electrodes 232 on the edge region of the second nitride film 224.The Schottky electrode part 240 may be formed to entirely cover thefirst ohmic electrodes 232 on the central region of the second nitridefilm 224. In addition, the Schottky electrode part 240 may be disposedto be spaced apart from the second ohmic electrode 234. Thus, theSchottky electrode part 240 and the first ohmic electrodes 232 may beconfigured in a prominence and depression structure in which they areengaged with one another in the semiconductor layer 220.

Meanwhile, the field plate 250 may be disposed on the semiconductorlayer 220 between the second ohmic electrode 234 and the Schottkyelectrode part 240. In this case, external side portions 252 of thefield plate 250 may be provided to be partially covered by the secondohmic electrode 234, and internal side portions 254 of the field plate250 may be provided to be partially covered by the edge portions 244 ofthe Schottky electrode part 240. The field plate 250 can provide aneffect of distributing an electric field concentrated on corner portionsof the Schottky electrode part 240 and the ohmic electrode part 230.

Continuously, a detailed description will be given of a method formanufacturing a semiconductor device 200 c in accordance with anothermodified embodiment of the present invention. FIGS. 27A to 27C are viewsshowing methods for manufacturing a semiconductor device 200 c havingbeen described with reference to FIGS. 25 and 26, respectively.

Referring to FIG. 27A, the base substrate 210 is prepared, and the firstnitride film 222 and the second nitride film 224 may be sequentiallyformed on the base substrate 210. The first nitride film 222 may includeGaN, and the second nitride film 224 may include AlGaN.

The field plate 250 may be formed. A step of forming the field plate 250may include a step of forming an insulating film on the second nitridefilm 224 in a conformal manner, a step of forming the first photoresistpattern PR1, which exposes a central region and edge regions of theinsulating film, on the insulating film, and a step of etching theinsulating film by using the first photoresist pattern PR1 as an etchingmask. Thus, the field plate 250 disposed between the central region andthe edge regions of the semiconductor layer 220 may be formed on thesemiconductor layer 220. After the field plate 250 is formed, the firstphotoresist pattern PR1 may be removed.

Referring to FIG. 27B, the ohmic electrode part 230 may be formed. Forexample, the first metal film may be formed that entirely covers theresultant field plate 250. Then, the second photoresist pattern PR2 maybe formed on the first metal film. The second photoresist pattern PR2can expose the first metal film on the middle regions A3 between thecentral region A1 and the edge regions A2. The part of the centralregion A1 may be a region excluding a region where the first ohmicelectrodes 232 are to be formed. In addition, the second photoresistpattern PR2 may be provided such that the first metal film on theexternal side portions 252 of the field plate 250 fails to be exposed.Thereafter, it is possible to etch the first metal film by using thesecond photoresist pattern PR2 as an etching mask. Thus, a plurality ofthe first ohmic electrodes 232 having an island-shaped cross section maybe formed in a lattice configuration on the central region A1 of thesemiconductor layer 220, and the second ohmic electrode 234 having aring shape may be formed on the edge regions A2 of the semiconductorlayer 220. Herein, the second ohmic electrode 234 may be formed topartially cover the external side portions 252 of the field plate 250.In this case, it is possible to distribute an electric fieldconcentrated on the corner portions of the second ohmic electrode 234being in contact with the field plate 250.

Referring to FIG. 27C, the Schottky electrode part 240 may be formed.For example, the second metal film may be formed on the resultant ohmicelectrode part 230. The second metal film may be a film of a metallicmaterial different from that of the first metal film for formation ofthe ohmic electrode part 230. It is possible to form the thirdphotoresist pattern PR3, which exposes a region B including a part ofthe edge regions A2 and the middle regions A3, on the second metal film.In addition, the third photoresist pattern PR3 may be provided such thatthe second metal film on the internal side portions 254 of the fieldplate 250 fails to be exposed. Thereafter, it is possible to etch thesecond metal film by using the third photoresist pattern PR3 as anetching mask. Thus, it is possible to form the Schottky electrode part240 which entirely covers the first ohmic electrodes 232 b on thecentral region A1 of the semiconductor layer 220. The Schottky electrodepart 240, entirely cover the first ohmic electrode part 232 b to therebyhave a prominence and depression structure in which they are engagedwith the first ohmic electrodes 232 b up and down, may be formed on thecentral region A1 of the semiconductor layer 220. Also, the Schottkyelectrode part 240 may be formed to partially cover the internal sideportions 254 of the field plate 250. In this case, it is possible todistribute an electric field concentrated on corner portions of theSchottky electrode part 240 being in contact with the field plate 250.

FIG. 28 is a view showing a semiconductor device in accordance withother embodiments of the present invention, and FIG. 29 is across-sectional view taken along a line IX-IX′ of FIG. 28.

Referring to FIGS. 28 and 29, a semiconductor device 200 d in accordancewith another modified embodiment of the present invention may include abase substrate 210, a semiconductor layer 220 a, an ohmic electrode part230, a Schottky electrode part 240 a, and a field plate 250. Thesemiconductor layer 220 may include a first nitride film 222 and asecond nitride film 224 sequentially stacked on the base substrate 210.A 2DEG may be generated on a boundary between the first and secondnitride films. The ohmic electrode part 230 may include a plurality offirst ohmic electrodes 232, and a second ohmic electrode 234, whereinthe first ohmic electrodes 232 are disposed on the central region of thesecond nitride film 22 and have an island shape cross section, and thesecond ohmic electrode 234 has a ring shape surrounding first ohmicelectrodes 232 on an edge region of the second nitride film 225. TheSchottky electrode part 240 may be formed to entirely cover the firstohmic electrodes 232 on the central region of the second nitride film225. In addition, the Schottky electrode part 240 may be disposed to bespaced apart from the second ohmic electrode 234. Thus, the Schottkyelectrode part 240 and the first ohmic electrodes 232 may be configuredto have a prominence and depression structure in which they are engagedwith one another in the semiconductor layer 220.

Meanwhile, the first and second bonding portions 242 a and 244 a of theSchottky electrode part 240 a may be extended to inside of the secondnitride film 225. For example, the first and second bonding portions 242a and 244 a may be extended downward from a top part of the secondnitride film 225, and may be disposed to be spaced apart from the firstnitride film 222. To this end, recesses 225 a may be provided in exposedparts of the second nitride film 225 on the middle region between thefirst ohmic electrodes 232 and the second ohmic electrode 234. Therecesses 225 a may be formed on the second nitride film 225 adjacent tothe first ohmic electrodes 232. The recesses 225 a may be formed on thesecond nitride film 225 between the first ohmic electrodes 232.

Also, the field plate 250 may be disposed on the semiconductor layer 220between the second ohmic electrode 234 and the Schottky electrode part240. In this case, external side portions 252 of the field plate 250 maybe provided to be partially covered by the second ohmic electrode 234,and internal side portions 254 of the field plate 250 may be provided tobe partially covered by the edge portions 244 of the Schottky electrodepart 240. The field plate 250 can provide an effect of distributing anelectric field concentrated on corner portions of the Schottky electrodepart 240 and the ohmic electrode part 230.

The semiconductor device 200 d may have a structure formed by combininga structure of the semiconductor device 200 a of one modified embodimentof the present invention with a structure of the semiconductor device200 c of another modified embodiment of the present invention.

Continuously, a detailed description will be given of a method formanufacturing a semiconductor device 100 d in accordance with anothermodified embodiment of the present invention. FIGS. 30A to 30C are viewsshowing methods for manufacturing the semiconductor device shown inFIGS. 28 and 29, respectively.

Referring to FIG. 30A, the base substrate 210 is prepared, and the firstnitride film 222 and the second nitride film 224 may be sequentiallyformed on the base substrate 210. The first nitride film 222 may includeGaN, and the second nitride film 224 may include AlGaN.

The field plate 250 may be formed. For example, a step of forming theinsulating film on the second nitride film 224 in a conformal manner, astep of forming the first photoresist pattern PR1, which exposes acentral region and an edge region of the insulating film, on theinsulating film, a step of etching the insulating film by using thefirst photoresist pattern PR1 as an etching mask, and a step of removingthe first photoresist pattern PR1 may be sequentially performed. Thus,the field plate 250 disposed between the central region and the edgeregions of the semiconductor layer 220 may be formed on thesemiconductor layer 220.

Referring to FIG. 30B, the ohmic electrode part 230 may be formed. Forexample, a step of forming the first metal film which covers allsurfaces of the resultant field plate 250, a step of forming the secondphotoresist pattern PR2 which partially exposes the first metal film, astep of etching the first metal film by using the second photoresistpattern PR2 as an etching mask, and a step of removing the secondphotoresist pattern PR2 may be sequentially performed. Herein, thesecond photoresist pattern PR2 may expose a region F on thesemiconductor layer 220, excluding a region where the first ohmicelectrodes 232 and the second ohmic electrode 234 are to be formed. Inthis case, the process of etching the first metal film may be an etchingprocess having an etching selection ratio for the field plates. Inaddition, the second photoresist pattern PR2 can be provided such thatthe first metal film on the external side portions 252 of the fieldplate 250 fails to be exposed. Thus, a plurality of first ohmicelectrodes 232 having island shape cross sections may be formed in alattice configuration on the central region A1 of the semiconductorlayer 220, and the second ohmic electrode 234 having a ring shape may beformed on the edge regions A2 of the semiconductor layer 220. Also, thesecond ohmic electrode 234 may be formed to partially cover the externalside portions 252 of the field plate 250.

Referring to FIG. 30C, the Schottky electrode part 240 a may be formed.For example, the second metal film may be formed on the resultant ohmicelectrode part 230. The second metal film may be a film composed of ametallic material different from that of the first metal film. The thirdphotoresist pattern PR3, which exposes regions B including a part of theedge regions A2 and the middle regions A3, may be formed on the secondmetal film. In addition, the third photoresist pattern PR3 may beprovided such that the second metal film on the internal side portions254 of the field plate 250 fails to be exposed. Thereafter, it ispossible to etch the second metal film by using the third photoresistpattern PR3 as an etching mask. Thus, the Schottky electrode part 240 aentirely covers the first ohmic electrodes 232 b on the central regionA1 of the semiconductor layer 220 to thereby have a prominence anddepression structure in which it is engaged with the first ohmicelectrodes 232 b up and down. The Schottky electrode part 240 a mayinclude the first bonding portions 242 a and the second bonding portion244 a, wherein the first bonding portions 242 a are bonded the firstohmic electrodes 232, and the second bonding portion 244 a are bonded tothe second nitride film 225 on the recesses 225 a.

Also, the Schottky electrode part 240 a may be formed to cover a part ofthe internal side portions 254 of the field plates 252.

FIG. 31 is a view showing other modified example of the semiconductordevice in accordance with another embodiment of the present invention.FIG. 32 is a cross-sectional view taken along a line X-X′ of FIG. 31.

Referring to FIGS. 31 and 32, the semiconductor device 200 e may includea base substrate 210, a semiconductor layer 220, an ohmic electrode part230 c, and a Schottky electrode part 240. The semiconductor layer 220may include the first nitride film 222 and the second nitride film 224sequentially stacked on the base substrate 210, and the 2DEG may beformed on the boundary surface between the nitride films.

The ohmic electrode part 230 c may include first ohmic electrodes 233and second ohmic electrode 234. Each of the first ohmic electrodes mayhave a ring shape based on the center 211 of the semiconductor layer220. For example, the first ohmic electrodes 233 may include firstelectrodes 233 a and a second electrode 233 b based on the center 211 ofthe semiconductor layer 220, and the second electrode 233 b may have adiameter bigger than those of the first electrodes 233 a. Also, thesecond ohmic electrode 234 may be provided to have a ring shapesurrounding the first ohmic electrodes 232 on the edge portion of thesecond nitride film 224. Thus, the first ohmic electrodes 233 and thesecond ohmic electrode 234 may mutually share the center 211 of thesemiconductor layer 220, and may have a ring shape with a mutuallydifferent diameter. The Schottky electrode part 240 may be formed toentirely cover the first ohmic electrodes 232 on the central region ofthe second nitride film 224. In addition, the Schottky electrode part240 may be disposed to be spaced apart from the second ohmic electrode234. Thus, the first ohmic electrodes 232 and the Schottky electrodepart 240 may be configured in a prominence and depression structure inwhich they are engaged with one another up and down.

The semiconductor device 200 e having the same structure may be providedwith the first ohmic electrodes with a ring-shaped cross section, incomparison with the semiconductor device 200 a in accordance with onemodified embodiment of the present invention. That is, the first ohmicelectrodes 233 and the second ohmic electrode may share the center ofthe semiconductor layer 220, and may be formed in a ring shape with amutually different diameter. Thus, the first ohmic electrodes 233 andthe second ohmic electrode 234 may be in an annual ring shape on thesemiconductor layer 220. Since those skilled in the art can enoughderive a process of forming the semiconductor device 200 e from themethods for manufacturing the semiconductor device of the presentinvention, the detailed description thereof will be omitted.

In the case where the semiconductor device of the present invention isdriven in a forward direction, when a driving voltage is higher than anon-votlge of the Schottky didoe, a current flows through an ohmicelectrodes and Schottky electrode portion at the same time. Further, acurrent flow by the first ohmic electrode posistoned below the Schottkyelectrode portion even if the driving voltage is lower than theon-voltage of the Schottky didoe. Therefore, in the semiconductordevice, forward currents are increased, and thus it is possible toperform operation even at a low driving voltage.

When the semiconductor device of the present invention is driven in areverse direction, a 2DEG is allowed to be disconnected by a depletionregion generated by the Schottky electrode portion to thereby stablyblock a current flow, which results in high reverse breakdown voltage.

In a method for manufacturing the semiconductor device, forward currentsare increased and reverse leakage currents are reduced, so that it ispossible to improve power converting efficiency of the semiconductordevice, as well as operation speed of the semiconductor device.

As described above, although the preferable embodiments of the presentinvention have been shown and described, it will be appreciated by thoseskilled in the art that substitutions, modifications and variations maybe made in these embodiments without departing from the principles andspirit of the general inventive concept, the scope of which is definedin the appended claims and their equivalents.

What is claimed is:
 1. A semiconductor device comprising: a basesubstrate; a semiconductor layer which is disposed on the base substrateand has a 2-Dimensional Electron Gas (2DEG) generated within thesemiconductor layer, the semiconductor layer comprising a first nitridefilm on the base substrate, the first nitride film being formed ofP-type having high resistivity, thereby reducing a leakage current ofthe semiconductor device, and a second nitride film which is disposed onthe first nitride film and has an energy band gap wider than that of thefirst nitride film; a plurality of first ohmic electrodes which aredisposed on the central region of the semiconductor layer and haveisland-shaped cross sections; a second ohmic electrode which is disposeddirectly on edge regions of the semiconductor layer, the second ohmicelectrode being formed in a ring shape surrounding the first ohmicelectrode; and a Schottky electrode part having first bonding portionsbonded to the first ohmic electrodes, and a second bonding portionbonded to the semiconductor layer, wherein a depletion region isprovided to be spaced apart from the 2DEG when the semiconductor deviceis driven at an on-voltage and is provided to be expanded to the 2DEGwhen the semiconductor device is driven at an off-voltage, the depletionregion being generated within the semiconductor layer by bonding thesemiconductor layer and the second bonding portion, the Schottkyelectrode part has a prominence and depression structure in which theSchottky electrode part is engaged with the first ohmic electrodes upand down.
 2. The semiconductor device of claim 1, wherein the firstbonding portions are bonded to the first ohmic electrodes on a top partof the first ohmic electrodes, and the second bonding portion is bondedto a region of the semiconductor layer adjacent to the first ohmicelectrodes.
 3. The semiconductor device of claim 1, wherein when thesemiconductor device is driven at a forward voltage equal to or higherthan the on-voltage of the Schottky electrode part, the depletion regionis provided to allow a current to flow from the Schottky electrode partto the 2DEG.
 4. The semiconductor device of claim 1, wherein, when thesemiconductor device is driven at a forward voltage lower than theon-voltage of the Schottky electrode part, the depletion region blocks acurrent flow from the Schottky electrode part to the 2DEG.
 5. Thesemiconductor device of claim 1, wherein, when the semiconductor deviceis driven at a reverse voltage, the depletion region blocks a currentflow from the first ohmic electrodes to the 2DEG.